This invention relates to a water-cooled, four-cycle internal combustion engine for outboard motors and more particularly to an improved arrangement for cooling the exhaust passages of such motors.
In connection with outboard motors, it has been the normal practice to route the exhaust gases from the engine downwardly through the drive shaft housing for discharge through an underwater exhaust. As a result, it is desirable to provide some effective degree of cooling of the exhaust gases before they are introduced into the drive shaft housing so as to reduce the likelihood of overheating. Furthermore, if the engine is of the four-cycle type, it has been the practice to route the exhaust gases through an internal passage formed in the cylinder head and cylinder block to their point of discharge. Hence, there is a fairly substantial degree of heating of the cylinder block itself by the exhaust gases and it is essential to provide adequate cooling so as to prevent distortion of the components and also so as to avoid failure of the cylinder head gasket. Although it has been proposed to provide a cooling jacket around the water passages, the cooling jackets of the type heretofore proposed may not always afforded the desired degree of cooling of the exhaust gases.
It is, therefore, a principal object of this invention to provide an improved water-cooled internal combustion engine for an outboard motor.
It is a further object of this invention to provide an improved cooling arrangement for cooling the exhaust gas passages of an outboard motor, particularly one operating on a four-stroke cycle.